Ceramic substrate and electronic component-embedded module

ABSTRACT

A ceramic substrate of the present disclosure is a ceramic substrate including a ceramic body having a ceramic layer on a surface thereof and a surface electrode placed on a primary face of the ceramic body. Between the surface electrode and the ceramic layer is an oxide layer made of an insulating oxide having a melting point higher than the firing temperature for the ceramic layer. The oxide layer also extends on the ceramic layer not occupied by the surface electrode. The oxide layer on the ceramic layer not occupied by the surface electrode has a rough surface.

This is a division of U.S. application Ser. No. 16/281,269 filed on Feb.21, 2019, which is a continuation of International Application No.PCT/JP2017/027723 filed on Jul. 31, 2017, which claims priority fromJapanese Patent Application No. 2016-161717 filed on Aug. 22, 2016. Thecontents of these applications are incorporated herein by reference intheir entireties.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to a ceramic substrate and an electroniccomponent-embedded module.

Description of the Related Art

Electronic component-embedded modules, formed by a ceramic substrate,multiple electronic components mounted thereon, and sealing resincovering the electronic components, have been used as highly functionalmodules, for example in electronic devices (e.g., see Patent Document1).

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 2005-183430

BRIEF SUMMARY OF THE DISCLOSURE

Those electronic component-embedded modules as described in PatentDocument 1 are disadvantageous in that firing in the production of theceramic substrate as an element of the module causes the glass componentof the ceramic layer to fuse out and cover a surface electrode on thesubstrate, affecting the function of the ceramic substrate.

One proposed way to control the covering of a surface electrode with theglass component is to fire the ceramic substrate with an alumina layeron the surface of the ceramic substrate.

Firing a ceramic substrate with an alumina layer on the surface of theceramic substrate as in the foregoing successfully limits the coveringof a surface electrode with the glass component. However, an electroniccomponent-embedded module the inventors fabricated using such a ceramicsubstrate was found to have the disadvantage of low adhesiveness betweenthe ceramic substrate and sealing resin.

In order to solve the above problem, the present disclosure is intendedto provide a ceramic substrate with controlled covering of a surfaceelectrode with a glass component and high adhesiveness to sealing resinin an electronic component-embedded module, and also to provide anelectronic component-embedded module including this ceramic substrate.

A ceramic substrate of the present disclosure is a ceramic substrateincluding a ceramic body having a ceramic layer on the surface thereofand a surface electrode placed on a primary face of the ceramic body.Between the surface electrode and the ceramic layer is an oxide layermade of an insulating oxide having a melting point higher than thefiring temperature for the ceramic layer. The oxide layer also extendson the ceramic layer not occupied by the surface electrode. The oxidelayer on the ceramic layer not occupied by the surface electrode has arough surface.

This ceramic substrate has an oxide layer made of an insulating oxidebetween a surface electrode and a ceramic layer. The oxide forming theoxide layer has a melting point higher than the firing temperature forthe ceramic layer and, therefore, does not melt while the ceramic layeris being fired. Any glass component that fuses out of the ceramic layerduring firing is therefore confined between the grains in the oxidelayer, limiting the covering of the surface electrode with a glasscomponent (hereinafter also referred to as wetting with glass).

The oxide layer also extends on the ceramic layer not occupied by thesurface electrode. However, the oxide layer on the ceramic layer notoccupied by the surface electrode has a rough surface, not smooth. Theceramic substrate has therefore a superior adhesion to the sealingresin, which is used when an electronic component-embedded module isfabricated.

In an embodiment, the surface roughness of the oxide layer on theceramic layer not occupied by the surface electrode is larger than thatof the oxide layer between the surface electrode and the ceramic layer.Such an arrangement provides an electronic component-embedded modulehaving a superior adhesion to the sealing resin.

This ceramic substrate can be produced by, for example, forming theoxide layer on the entire surface of the ceramic layer, forming thesurface electrode on part of the oxide layer, and then roughening thesurface of the oxide on the ceramic layer not occupied by the surfaceelectrode.

In an embodiment, the oxide layer between the surface electrode and theceramic layer also has a rough surface. Such an arrangement provides anelectronic component-embedded module having a superior adhesion to thesealing resin.

This ceramic substrate can be produced by, for example, forming theoxide layer on the entire surface of the ceramic layer withlarge-diameter oxide particles in the oxide layer and then forming thesurface electrode on a part of the oxide layer.

A ceramic substrate of the present disclosure is a ceramic substrateincluding a ceramic body having a ceramic layer on the surface thereofand a surface electrode placed on a primary face of the ceramic body.Between the surface electrode and the ceramic layer is an oxide layermade of an insulating oxide having a melting point higher than thefiring temperature for the ceramic layer. The surface of the ceramiclayer not occupied by the surface electrode is exposed.

This ceramic substrate has an oxide layer made of an insulating oxidebetween a surface electrode and a ceramic layer. This limits thecovering of the surface electrode with a glass component.

On the ceramic layer not occupied by the surface electrode, the oxidelayer is not present, and the surface of the ceramic layer is exposed.The ceramic substrate has therefore a superior adhesion to the sealingresin, which is used when an electronic component-embedded module isfabricated.

In the ceramic substrate of the present disclosure, the oxide layer ispreferably an alumina layer.

The ceramic layer usually contains alumina in many cases. In such acase, any reaction between the alumina layer and the ceramic layerduring firing only produces compounds that can be formed inside theceramic layer. The reaction therefore produces no extraneous compound.Hence, it is unlikely that such a reaction affects the quality of theceramic substrate.

An electronic component-embedded module of the present disclosureincludes a ceramic substrate of the present disclosure, an electroniccomponent mounted on the surface electrode of the ceramic substrate, andsealing resin placed on a primary face of the ceramic substrate to coverthe electronic component.

As stated above, the ceramic substrate of the present disclosure has asuperior adhesion to the sealing resin. The sealing resin therefore doesnot easily come off the ceramic substrate even if a transverse force(parallel to the primary faces of the ceramic substrate) is applied tothe electronic component-embedded module.

According to the present disclosure, there is provided a ceramicsubstrate with controlled covering of a surface electrode with a glasscomponent and high adhesiveness to the sealing resin in an electroniccomponent-embedded module.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram schematically illustrating anexample of a ceramic substrate according to Embodiment 1 of the presentdisclosure.

FIGS. 2A, 2B, 2C, and 2D are cross-sectional diagrams schematicallyillustrating an example of a method for producing the ceramic substrate1 illustrated in FIG. 1.

FIG. 3 is a cross-sectional diagram schematically illustrating anexample of an electronic component-embedded module according toEmbodiment 1 of the present disclosure.

FIG. 4 is a cross-sectional diagram schematically illustrating anexample of a ceramic substrate according to Embodiment 2 of the presentdisclosure.

FIGS. 5A, 5B, and 5C are cross-sectional diagrams illustrating anexample of a method for producing the ceramic substrate 2 illustrated inFIG. 4.

FIG. 6 is a cross-sectional diagram schematically illustrating anexample of an electronic component-embedded module according toEmbodiment 2 of the present disclosure.

FIG. 7 is a cross-sectional diagram schematically illustrating anexample of a ceramic substrate according to Embodiment 3 of the presentdisclosure.

FIGS. 8A, 8B, and 8C are cross-sectional diagrams illustrating anexample of a method for producing the ceramic substrate 3 illustrated inFIG. 7.

FIG. 9 is a cross-sectional diagram schematically illustrating anexample of an electronic component-embedded module according toEmbodiment 3 of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The following describes embodiments of the ceramic substrates andelectronic component-embedded modules of the present disclosure.

The present disclosure, however, is not limited to the followingconfigurations and can be applied with any necessary modificationswithin the scope of the present disclosure.

Combinations of two or more desirable configurations from separateembodiments set forth below are also encompassed in the presentdisclosure.

Needless to say, the embodiments presented hereinafter are illustrative,and partial replacement or combination of configurations described indifferent embodiments is possible. The second and later embodiments skipover anything in common with Embodiment 1 and describe only differences.In particular, similar advantages resulting from similar configurationsare not mentioned one by one in each embodiment.

Embodiment 1 (Ceramic Substrate)

A ceramic substrate according to Embodiment 1 of the present disclosureincludes a ceramic body having a ceramic layer on its surface and asurface electrode placed on a primary face of the ceramic body. Betweenthe surface electrode and the ceramic layer is an oxide layer made of aninsulating oxide having a melting point higher than the firingtemperature for the ceramic layer.

In Embodiment 1 of the present disclosure, there is an oxide layer madeof an insulating oxide having a melting point higher than the firingtemperature for the ceramic layer not only between the surface electrodeand the ceramic layer but also on the ceramic layer not occupied by thesurface electrode. The oxide layer on the ceramic layer not occupied bythe surface electrode has a rough surface, and the surface roughness ofthe oxide layer on the ceramic layer not occupied by the surfaceelectrode is larger than that of the oxide layer between the surfaceelectrode and the ceramic layer.

FIG. 1 is a cross-sectional diagram schematically illustrating anexample of a ceramic substrate according to Embodiment 1 of the presentdisclosure.

Although its entire structure is not illustrated in FIG. 1, the ceramicsubstrate 1 includes a ceramic body 10 having a ceramic layer 11 on itssurface and a surface electrode 20 placed on a primary face of theceramic body 10.

The ceramic substrate 1 illustrated in FIG. 1 has an oxide layer 31between the surface electrode 20 and the ceramic layer 11, plus an oxidelayer 32 on the ceramic layer 11 not occupied by the surface electrode20. The oxide layer 32 on the ceramic layer 11 not occupied by thesurface electrode 20 has a rough surface, and the surface roughness ofthe oxide layer 32 is larger than that of the oxide layer 31 between thesurface electrode 20 and the ceramic layer 11.

Although not illustrated in FIG. 1, the ceramic body 10 has a multilayerstructure in which multiple ceramic layers 11 are stacked. Inside theceramic body 10, there are inner-layer conductors and via conductors.There may be a surface electrode on the other primary face of theceramic body 10.

The ceramic layers forming the ceramic body preferably contain alow-temperature-sintering ceramic material. Low-temperature-sinteringceramic materials represent ceramic materials that sinter at firingtemperatures of 1000° C. or lower and can be cofired with, for example,Ag or Cu.

Examples of low-temperature-sintering ceramic materials that can becontained in the ceramic layers include glass-compositelow-temperature-sintering ceramic materials, produced by mixingborosilicate glass into quartz, alumina, forsterite, or a similarceramic material; crystallized-glass low-temperature-sintering ceramicmaterials, made using crystallized glass of the ZnO—MgO—Al₂O₃—SiO₂system; and non-glass low-temperature-sintering ceramic materials, madeusing a ceramic material of the BaO—Al₂O₃—SiO₂, Al₂O₃—CaO—SiO₂—MgO—B₂O₃,or a similar system. For the prevention of the formation of extraneouscompounds upon the reaction with the oxide layers, it is preferred thatthe low-temperature-sintering ceramic material contain the oxide thatforms the oxide layers, more preferably alumina.

The inner-layer conductors and via conductors, placed inside the ceramicbody, contain an electrically conductive component. Examples ofelectrically conductive components that can be contained in theinner-layer conductors and via conductors include Au, Ag, Cu, Pt, Ta, W,Ni, Fe, Cr, Mo, Ti, Pd, Ru, and alloys based on one of these metals. Theinner-layer conductors and via conductors preferably contain Au, Ag, orCu, more preferably Ag or Cu, as the electrically conductive component.Owing to their low resistance, Au, Ag, and Cu are suitable especially inhigh-frequency applications.

The surface electrode, placed on a primary face of the ceramic body, isto be connected to an electronic component and contains an electricallyconductive component. Examples of electrically conductive componentsthat can be contained in the surface electrode include Au, Ag, Cu, Pt,Ta, W, Ni, Fe, Cr, Mo, Ti, Pd, Ru, and alloys based on one of thesemetals. The surface electrode preferably contains the same electricallyconductive component as the inner-layer conductors and via conductors.Specifically, the surface electrode preferably contains Au, Ag, or Cu,more preferably Ag or Cu, as the electrically conductive component.

The surface electrode may contain components other than the electricallyconductive component, but for the prevention of covering with a glasscomponent, it is preferred that the surface electrode containsubstantially no glass component.

The oxide layers, between the surface electrode and the ceramic layerand on the ceramic layer not occupied by the surface electrode, are bothmade of an insulating oxide that has a melting point higher than thefiring temperature for the ceramic layers.

The melting point of the oxide forming the oxide layers is preferablyhigher than 1000° C., more preferably higher than 1800° C., even morepreferably higher than 2000° C. The melting point of the oxide formingthe oxide layers is preferably equal to or lower than 3000° C. Specificexamples of the oxide layers include alumina layers, titania layers,zirconia layers, silica layers, and magnesia layers. Of these, aluminalayers are preferred.

In Embodiment 1 of the present disclosure, a requirement is that thesurface roughness of the oxide layer on the ceramic layer not occupiedby the surface electrode be larger than that of the oxide layer betweenthe surface electrode and the ceramic layer. The surface roughness ofthe oxide layer on the ceramic layer not occupied by the surfaceelectrode is therefore not critical in itself, but preferably is 1 μm ormore and 10 μm or less. A surface roughness in this range results ingreater adhesiveness to the resin.

Here, the surface roughness represents the maximum height (Rz) asdefined in JIS B 0601-2001 and is obtained with the cut-off wavelengthλc=0.250 mm to remove the surface waviness component.

In Embodiment 1 of the present disclosure, the thickness of the oxidelayers is not critical, but preferably is 1 μm or more and 10 μm orless. A thickness in this range will ensure the effective prevention ofwetting with glass.

Here, the thickness of the oxide layers is obtained by microscopicallymeasuring a cross-section exposed by grinding.

In Embodiment 1 of the present disclosure, the oxide layers preferablyextend over the entire surface of the ceramic layer. However, the rangeof the oxide layers is not critical as long as they extend between thesurface electrode and the ceramic layer and on the ceramic layer notoccupied by the surface electrode.

The ceramic substrate 1 illustrated in FIG. 1 is preferably produced asfollows.

FIGS. 2A, 2B, 2C, and 2D are cross-sectional diagrams schematicallyillustrating an example of a method for producing the ceramic substrate1 illustrated in FIG. 1.

First, multiple ceramic green sheets are prepared. The ceramic greensheets are to be fired into ceramic layers.

The ceramic green sheets are sheets obtained by shaping, for example bydoctor blading, a slurry containing a powder of ceramic raw material,such as a low-temperature-sintering ceramic material, an organic binder,and a solvent. The slurry may contain additives, such as a dispersantand a plasticizer.

Particular ceramic green sheets are perforated with through holes forvia conductors. These through holes are filled with an electricallyconductive paste conducting, for example, Ag or Cu as the electricallyconductive component to form pieces of electrically conductive pastethat will later become via conductors.

Using an electrically conductive paste having the same formula as theabove one, layers of electrically conductive paste that will laterbecome inner-layer conductors are formed on particular ceramic greensheets, for example by screen printing.

Then, as illustrated in FIG. 2A, an oxide layer 30 having a smoothsurface is formed on the ceramic green sheet 11′ that will be positionedat the surface after stacking. In FIG. 2A, the oxide layer 30 has beenformed on the entire surface of the ceramic green sheet 11′. The oxidelayer 30 can be formed using a paste containing an oxide, such asalumina, for example by screen printing. The oxide layer 30 may beformed after the ceramic green sheets 11′ are stacked.

For controlled covering of the surface electrode with a glass component,it is preferred that the oxide particles forming the oxide layer bedensely packed. For example, it is preferred that the diameters of theoxide particles, such as alumina particles, be 0.1 μm or more and 1 μmor less.

The thickness of the oxide layer formed on the ceramic green sheet isnot critical, but preferably is 1 μm or more and 10 μm or less. Athickness in this range will ensure the effective prevention of wettingwith glass.

As illustrated in FIG. 2B, an electrically conductive paste layer 20′that will later become a surface electrode 20 is formed on a part of theoxide layer 30. The electrically conductive paste layer 20′ can beformed by screen printing or a similar technique, for example using anelectrically conductive paste having the same formula as those mentionedabove. Then, the multiple ceramic green sheets 11′ are stacked andpressure-bonded. In this way, an unfired multilayer body 1′ is produced.

Then, the unfired multilayer body 1′ is fired. This gives a multilayerbody that includes, as illustrated in FIG. 2C, a ceramic body 10 havinga ceramic layer 11 on its surface, an oxide layer 30 formed over thewhole area of a primary face of the ceramic body 10, and a surfaceelectrode 20 formed on the oxide layer 30.

In FIG. 2C, the oxide layer 30 has been formed not only between thesurface electrode 20 and the ceramic layer 11 but also on the ceramiclayer 11 not occupied by the surface electrode 20, and its surface issmooth. The oxide layer 30 on the surface of the ceramic layer 11 limitsthe covering of the surface electrode 20 with a glass component,ensuring the electrical conductivity of the surface electrode 20.

The firing of the multilayer body may be performed using a beddingpowder. Moreover, the ceramic multilayer body may be divided before orafter firing.

Then, the surface of the fired multilayer body is roughened. This gives,as illustrated in FIG. 2D, the oxide layer 32 on the ceramic layer 11not occupied by the surface electrode 20 a rough surface, and thesurface roughness of the oxide layer 32 on the ceramic layer 11 notoccupied by the surface electrode 20 becomes larger than that of theoxide layer 31 between the surface electrode 20 and the ceramic layer11. This leads to the improved adhesion to the sealing resin, which isused when an electronic component-embedded module is fabricated.

The method for roughening can be, for example, grinding or spraying withan abrasive. The surface of the surface electrode may be roughenedunless it has negative impact on the surface electrode. Masking mayoptionally be performed.

In Embodiment 1 of the present disclosure, the surface roughness of theoxide layer on the ceramic layer not occupied by the surface electrodecan be about 5 μm.

The fired multilayer body may be subjected to electroplating orelectroless plating to form a plating layer on the top of the surfaceelectrode.

In this way, the ceramic substrate 1 illustrated in FIG. 1 is obtained.

Note that the unfired multilayer body may be fired with a restraininggreen sheet, prepared beforehand and containing an oxide that is notsubstantially sintered at the temperature at which the ceramic greensheets are sintered, on both primary faces of the multilayer body.

In this case, the restraining green sheets do not shrink but rather helplimit the shrinkage of the multilayer body in the direction parallel tothe primary faces because they are not substantially sintered whenfired. As a result, the size accuracy of the ceramic substrate 1 isimproved.

The restraining green sheets are preferably sheets obtained by shaping,for example by doctor blading, a slurry containing a powder of an oxideof the aforementioned type, an organic binder, and a solvent. The slurrymay contain additives, such as a dispersant and a plasticizer.

Examples of oxides that can be contained in the slurry include alumina,titania, zirconia, silica, and magnesia. Of these, it is preferred touse the same oxide as that forming the oxide layers, more preferablyalumina.

(Electronic Component-Embedded Module)

FIG. 3 is a cross-sectional diagram schematically illustrating anexample of an electronic component-embedded module according toEmbodiment 1 of the present disclosure.

The electronic component-embedded module 100 illustrated in FIG. 3includes a ceramic substrate 1, an electronic component 40 mounted onthe surface electrodes 20 of the ceramic substrate 1, and sealing resin50 placed on a primary face of the ceramic substrate 1 to cover theelectronic component 40. The ceramic substrate 1 illustrated in FIG. 3has two surface electrodes 20 but otherwise has the same structure asthe ceramic substrate 1 illustrated in FIG. 1.

As stated above, the ceramic substrate 1 has a rough-surfaced oxidelayer 32 on the ceramic layer 11 not occupied by the surface electrodes20. The ceramic substrate 1 has therefore a superior adhesion to thesealing resin 50, and the sealing resin 50 does not easily come off theceramic substrate 1 even if a transverse force (parallel to the primaryfaces of the ceramic substrate 1) is applied to the electroniccomponent-embedded module 100.

The surface electrodes and the electronic component are connected by,for example, soldering. The electronic component is, for example, anactive component, a passive component, or a composite thereof. Examplesof active components include semiconductor devices, such as atransistor, a diode, an IC, or an LSI device. Examples of passivedevises include chip components, such as a resistor, a capacitor, and aninductor, oscillators, and filters.

The sealing resin can be of any material, but examples of potentialmaterials include curable resins, such as epoxy resin and polyimideresins.

The sealing resin is preferably placed in a half-melted state on theelectronic component and then solidified or cured. Although in FIG. 3there is some sealing resin between the ceramic substrate and theelectronic component, the space between the ceramic substrate and theelectronic component may be filled with the sealing resin or may be leftvacant, with no sealing resin there.

Embodiment 2 (Ceramic Substrate)

As in Embodiment 1 of the present disclosure, a ceramic substrateaccording to Embodiment 2 of the present disclosure includes a ceramicbody having a ceramic layer on its surface and a surface electrodeplaced on a primary face of the ceramic body. Between the surfaceelectrode and the ceramic layer is an oxide layer made of an insulatingoxide having a melting point higher than the firing temperature for theceramic layer.

In Embodiment 2 of the present disclosure, there is an oxide layer madeof an insulating oxide having a melting point higher than the firingtemperature for the ceramic layer not only between the surface electrodeand the ceramic layer but also on the ceramic layer not occupied by thesurface electrode. The oxide layer on the ceramic layer not occupied bythe surface electrode has a rough surface, and the oxide layer betweenthe surface electrode and the ceramic layer also has a rough surface.

FIG. 4 is a cross-sectional diagram schematically illustrating anexample of a ceramic substrate according to Embodiment 2 of the presentdisclosure.

Although its entire structure is not illustrated in FIG. 4, the ceramicsubstrate 2 includes a ceramic body 10 having a ceramic layer 11 on itssurface and a surface electrode 20 placed on a primary face of theceramic body 10.

The ceramic substrate 2 illustrated in FIG. 4 has an oxide layer 33between the surface electrode 20 and the ceramic layer 11, plus an oxidelayer 34 on the ceramic layer 11 not occupied by the surface electrode20. The oxide layer 34 on the ceramic layer 11 not occupied by thesurface electrode 20 has a rough surface, and the oxide layer 33 betweenthe surface electrode 20 and the ceramic layer 11 also has a roughsurface.

The structure of the ceramic body and the surface electrode is the sameas in Embodiment 1.

The oxide layers, between the surface electrode and the ceramic layerand on the ceramic layer not occupied by the surface electrode, are bothmade of an insulating oxide that has a melting point higher than thefiring temperature for the ceramic layers.

The melting point of the oxide forming the oxide layers is preferablyhigher than 1000° C., more preferably higher than 1800° C., even morepreferably higher than 2000° C. The melting point of the oxide formingthe oxide layers is preferably equal to or lower than 3000° C. Specificexamples of oxide layers include alumina layers, titania layers,zirconia layers, silica layers, and magnesia layers. Of these, aluminalayers are preferred.

In Embodiment 2 of the present disclosure, a requirement is that theoxide layer on the ceramic layer not occupied by the surface electrodeand the oxide layer between the surface electrode and the ceramic layerhave a rough surface. The surface roughness of each oxide layer istherefore not critical in itself, but preferably is 1 μm or more and 10μm or less. A surface roughness in this range results in greateradhesiveness to the resin. Note that the surface roughness of the oxidelayer on the ceramic layer not occupied by the surface electrode may bethe same as or different from that of the oxide layer between thesurface electrode and the ceramic layer.

In Embodiment 2 of the present disclosure, the thickness of the oxidelayers is not critical, but preferably is 1 μm or more and 10 μm orless. A thickness in this range will ensure the effective prevention ofwetting with glass.

In Embodiment 2 of the present disclosure, the oxide layers preferablyextend over the entire surface of the ceramic layer. However, the rangeof the oxide layers is not critical as long as they extend between thesurface electrode and the ceramic layer and on the ceramic layer notoccupied by the surface electrode.

The ceramic substrate 2 illustrated in FIG. 4 is preferably produced asfollows.

FIGS. 5A, 5B, and 5C are cross-sectional diagrams schematicallyillustrating an example of a method for producing the ceramic substrate2 illustrated in FIG. 4.

First, as in Embodiment 1, multiple ceramic green sheets are prepared,and then particular ceramic green sheets have pieces of electricallyconductive paste, which will later become via conductors, formedtherethrough or have layers of electrically conductive paste, which willlater become inner-layer conductors, formed thereon.

Then, as illustrated in FIG. 5A, an oxide layer 30′ having a roughsurface is formed on the ceramic green sheet 11′ that will be positionedat the surface after stacking. In FIG. 5A, the oxide layer 30′ has beenformed on the entire surface of the ceramic green sheet 11′. The oxidelayer 30′ can be formed using a paste containing an oxide, such asalumina, for example by screen printing. The oxide layer 30′ may beformed after the ceramic green sheets 11′ are stacked.

For controlled covering of the surface electrode with a glass component,it is preferred that the oxide particles forming the oxide layer bedensely packed. Incidentally, the prior addition to the paste of oxideparticles larger than the thickness of the oxide layer to be formed willgive the oxide layer a rough surface by leaving projections on thesurface of the oxide layer after firing. For example, if an about 3-μmthick oxide layer is formed, it is preferred to add beforehand oxideparticles having a diameter of 5 μm or more and 10 μm or less (largerparticles) to oxide particles having a diameter of 0.1 μm or more and 1μm or less (smaller particles). The size of the larger particles, thesize of the smaller particles, the proportion of the larger to smallerparticles, etc., can be adjusted according to the desired adhesivenessto sealing resin.

In Embodiment 2 of the present disclosure, the surface roughness of theoxide layer can be about 2 μm.

The thickness of the oxide layer formed on the ceramic green sheet isnot critical, but preferably is 1 μm or more and 10 μm or less. Athickness in this range will ensure the effective prevention of wettingwith glass.

As illustrated in FIG. 5B, an electrically conductive paste layer 20′that will later become a surface electrode 20 is formed on a part of theoxide layer 30′ in a similar way as in Embodiment 1. Then, the multipleceramic green sheets 11′ are stacked and pressure-bonded. In this way,an unfired multilayer body 2′ is produced.

Then, the unfired multilayer body 2′ is fired. This gives a multilayerbody that includes, as illustrated in FIG. 5C, a ceramic body 10 havinga ceramic layer 11 on its surface, oxide layers 33, 34 formed over thewhole area of a primary face of the ceramic body 10, and a surfaceelectrode 20 formed on the oxide layer 33. Note that the oxide layers33, 34 illustrated in FIG. 5C are the same as the oxide layer 30′illustrated in FIGS. 5A and 5B.

In FIG. 5C, not only the oxide layer 34 on the ceramic layer 11 notoccupied by the surface electrode 20 but also the oxide layer 33 betweenthe surface electrode 20 and the ceramic layer 11 has a rough surface.The oxide layers 33, 34 on the surface of the ceramic layer 11 limit thecovering of the surface electrode 20 with a glass component, ensuringthe electrical conductivity of the surface electrode 20. Moreover, theoxide layer 34 on the ceramic layer 11 not occupied by the surfaceelectrode 20 has a rough surface, and this leads to the improvedadhesion to the sealing resin, which is used when an electroniccomponent-embedded module is fabricated.

The fired multilayer body may be subjected to electroplating orelectroless plating to form a plating layer on the top of the surfaceelectrode.

In this way, the ceramic substrate 2 illustrated in FIG. 4 is obtained.

Note that the unfired multilayer body may be fired with a restraininggreen sheet, prepared beforehand and containing an oxide that is notsubstantially sintered at the temperature at which the ceramic greensheets are sintered, on both primary faces of the multilayer body.

(Electronic Component-Embedded Module)

FIG. 6 is a cross-sectional diagram schematically illustrating anexample of an electronic component-embedded module according toEmbodiment 2 of the present disclosure.

The electronic component-embedded module 200 illustrated in FIG. 6includes a ceramic substrate 2, an electronic component 40 mounted onthe surface electrodes 20 of the ceramic substrate 2, and sealing resin50 placed on a primary face of the ceramic substrate 2 to cover theelectronic component 40. The ceramic substrate 2 illustrated in FIG. 6has two surface electrodes 20 but otherwise has the same structure asthe ceramic substrate 2 illustrated in FIG. 4.

As stated above, the ceramic substrate 2 has a rough-surfaced oxidelayer 34 on the ceramic layer 11 not occupied by the surface electrodes20. The ceramic substrate 2 has therefore a superior adhesion to thesealing resin 50, and the sealing resin 50 does not easily come off theceramic substrate 2 even if a transverse force (parallel to the primaryfaces of the ceramic substrate 2) is applied to the electroniccomponent-embedded module 200.

Embodiment 3 (Ceramic Substrate)

As in Embodiment 1 of the present disclosure, a ceramic substrateaccording to Embodiment 3 of the present disclosure includes a ceramicbody having a ceramic layer on its surface and a surface electrodeplaced on a primary face of the ceramic body. Between the surfaceelectrode and the ceramic layer is an oxide layer made of an insulatingoxide having a melting point higher than the firing temperature for theceramic layer.

In Embodiment 3 of the present disclosure, there is no oxide layer, andtherefore the surface is exposed, on the ceramic layer not occupied bythe surface electrode.

FIG. 7 is a cross-sectional diagram schematically illustrating anexample of a ceramic substrate according to Embodiment 3 of the presentdisclosure.

Although its entire structure is not illustrated in FIG. 7, the ceramicsubstrate 3 includes a ceramic body 10 having a ceramic layer 11 on itssurface and a surface electrode 20 placed on a primary face of theceramic body 10.

The ceramic substrate 3 illustrated in FIG. 7 has an oxide layer 35between the surface electrode 20 and the ceramic layer 11, and thesurface of the ceramic layer 11 not occupied by the surface electrode 20is exposed.

The structure of the ceramic body and the surface electrode is the sameas in Embodiment 1.

The oxide layer, between the surface electrode and the ceramic layer, ismade of an insulating oxide that has a melting point higher than thefiring temperature for the ceramic layers.

The melting point of the oxide forming the oxide layer is preferablyhigher than 1000° C., more preferably higher than 1800° C., even morepreferably higher than 2000° C. The melting point of the oxide formingthe oxide layer is preferably equal to or lower than 3000° C. Specificexamples of oxide layers include an alumina layer, a titania layer, azirconia layer, a silica layer, and a magnesia layer. Of these, analumina layer is preferred.

In Embodiment 3 of the present disclosure, the thickness of the oxidelayer is not critical, but preferably is 1 μm or more and 10 μm or less.A thickness in this range will ensure the effective prevention ofwetting with glass.

In Embodiment 3 of the present disclosure, the size of the oxide layeris not critical as long as the oxide layer is present between thesurface electrode and the ceramic layer.

The ceramic substrate 3 illustrated in FIG. 7 is preferably produced asfollows.

FIGS. 8A, 8B, and 8C are cross-sectional diagrams schematicallyillustrating an example of a method for producing the ceramic substrate3 illustrated in FIG. 7.

First, as in Embodiment 1, multiple ceramic green sheets are prepared,and then particular ceramic green sheets have pieces of electricallyconductive paste, which will later become via conductors, formedtherethrough or have layers of electrically conductive paste, which willlater become inner-layer conductors, formed thereon.

Then, as illustrated in FIG. 8A, an oxide layer 35 having a smoothsurface is formed on the ceramic green sheet 11′ that will be positionedat the surface after stacking. The oxide layer 35 can be formed using apaste containing an oxide, such as alumina, for example by screenprinting. The oxide layer 35 may be formed after the ceramic greensheets 11′ are stacked.

For controlled covering of the surface electrode with a glass component,it is preferred that the oxide particles forming the oxide layer bedensely packed. For example, it is preferred that the diameters of theoxide particles, such as alumina particles, be 0.1 μm or more and 1 μmor less.

The thickness of the oxide layer formed on the ceramic green sheet isnot critical, but preferably is 1 μm or more and 10 μm or less. Athickness in this range will ensure the effective prevention of wettingwith glass.

As illustrated in FIG. 8B, an electrically conductive paste layer 20′that will later become a surface electrode 20 is formed the oxide layer35 in a similar way as in Embodiment 1. In doing this, using the samescreen as for the formation of the oxide layer 35 will ensure that theapplied paste fits the oxide layer 35. Then, the multiple ceramic greensheets 11′ are stacked and pressure-bonded. In this way, an unfiredmultilayer body 3′ is produced.

Then, the unfired multilayer body 3′ is fired. This gives a multilayerbody that includes, as illustrated in FIG. 8C, a ceramic body 10 havinga ceramic layer 11 on its surface, an oxide layer 35 formed on part of aprimary face of the ceramic body 10, and a surface electrode 20 formedon the oxide layer 35.

In FIG. 8C, an oxide layer 35 has been formed between the surfaceelectrode 20 and the ceramic layer 11, and the surface of the ceramiclayer 11 not occupied by the surface electrode 20 is exposed. The oxidelayer 35 on the surface of the ceramic layer 11 limits the covering ofthe surface electrode 20 with a glass component, ensuring the electricalconductivity of the surface electrode 20. Moreover, the exposed surfaceof the ceramic layer 11 not occupied by the surface electrode 20provides the improved adhesion to the sealing resin, which is used whenan electronic component-embedded module is fabricated.

The fired multilayer body may be subjected to electroplating orelectroless plating to form a plating layer on the top of the surfaceelectrode.

In this way, the ceramic substrate 3 illustrated in FIG. 7 is obtained.

Note that the unfired multilayer body may be fired with a restraininggreen sheet, prepared beforehand and containing an oxide that is notsubstantially sintered at the temperature at which the ceramic greensheets are sintered, on both primary faces of the multilayer body.

(Electronic Component-Embedded Module)

FIG. 9 is a cross-sectional diagram schematically illustrating anexample of an electronic component-embedded module according toEmbodiment 3 of the present disclosure.

The electronic component-embedded module 300 illustrated in FIG. 9includes a ceramic substrate 3, an electronic component 40 mounted onthe surface electrodes 20 of the ceramic substrate 3, and sealing resin50 placed on a primary face of the ceramic substrate 3 to cover theelectronic component 40. The ceramic substrate 3 illustrated in FIG. 9has two surface electrodes 20 but otherwise has the same structure asthe ceramic substrate 3 illustrated in FIG. 7.

As stated above, the ceramic substrate 3 has an exposed surface on theceramic layer 11 not occupied by the surface electrodes 20. The ceramicsubstrate 3 has therefore a superior adhesion to the sealing resin 50,and the sealing resin 50 does not easily come off the ceramic substrate3 even if a transverse force (parallel to the primary faces of theceramic substrate 3) is applied to the electronic component-embeddedmodule 300.

Other Embodiments

Ceramic substrates and electronic component-embedded modules of thepresent disclosure are not limited to the above embodiments. Variousmodifications and variations are possible within the scope of thedisclosure, for example for the structure of the ceramic body and thesurface electrode and the method for forming the oxide layer(s).

-   -   1, 2, 3 Ceramic substrate    -   10 Ceramic body    -   11 Ceramic layer    -   20 Surface electrode    -   30, 30′, 31, 32, 33, 34, 35 Oxide layer    -   40 Electronic component    -   50 Sealing resin    -   100, 200, 300 Electronic component-embedded module

1. A ceramic substrate comprising a ceramic body having a ceramic layeron a surface thereof; and a surface electrode on a primary face of theceramic body, wherein: the ceramic substrate further comprises an oxidelayer provided between the surface electrode and the ceramic layer,wherein the oxide layer includes an insulating oxide having a meltingpoint higher than a firing temperature for the ceramic layer; and asurface of the ceramic layer not occupied by the surface electrode isexposed.
 2. The ceramic substrate according to claim 1, wherein theoxide layer is an alumina layer.
 3. An electronic component-embeddedmodule comprising: the ceramic substrate according to claim 1; anelectronic component mounted on the surface electrode of the ceramicsubstrate; and a sealing resin placed on the primary face of the ceramicsubstrate to cover the electronic component.